This invention relates to a DC power supply apparatus useable with arc-utilizing apparatuses, such as an arc welder, an arc cutter or a discharge lamp ignition apparatus, and, more particularly, to such DC power supply apparatus operable from any one of a plurality of AC voltages.
A DC power supply apparatus for use with an arc-utilizing apparatus is frequently operated from a commercial AC power supply. There are commercial AC power supplies supplying voltages of different magnitudes. For example, there are power supplies supplying higher voltages of, for example, 380 V, 400 V, 410 V, 460 V and 575 V, which form a higher voltage group, and there are power supplies supplying lower voltages of, for example, 200 V, 208 V, 230 V and 240 V, which form a lower voltage group. DC power supply apparatuses are designed to convert a local commercial AC voltage into a DC voltage. On the other hand, there are areas including regions where a high commercial AC voltage is supplied and regions where a low commercial AC voltage is supplied. Accordingly, a user must be very careful to determine which one of DC power supply apparatuses should be used, a high-voltage type or a low-voltage type. Therefore, a DC power supply apparatus operable either from a higher-voltage supplying commercial AC power supply or a lower-voltage supplying commercial AC power supply has been long desired.
An example of such DC power supply apparatuses is disclosed in U.S. Pat. No. 6,054,674 issued on Apr. 25, 2000 to Haruo Moriguchi et al., entitled xe2x80x9cDC Power Supply Apparatus for Arc-Utilizing Apparatusesxe2x80x9d, which corresponds to Japanese Patent Application Publication No. HEI 11-206123 A published on Jul. 30, 1999. The circuit diagram of the power supply apparatus disclosed in this U.S. patent is shown in FIG. 1. The DC power supply apparatus has power supply input terminals 1a, 1b and 1c. 
Let it be assumed that one of the voltages in the lower commercial AC voltage group is applied to the power supply input terminals 1a-1c. The AC voltage is coupled to an input-side rectifier 3 through switches 2a, 2b and 2c, where it is rectified. A switch control unit 30 judges that the low AC voltage is being applied to the input terminals 1a-1c. The judgment made by the switch control unit 30 is provided to a voltage-lowering converter control unit 9, in response to which the control unit 9 sends a command to a thyristor control unit 11 for turning on a thyristor 10. At the same time, the switch control unit 30 opens a normally-closed switch 12a and closes normally-open switches 12b and 12c, which causes smoothing capacitors 8a and 8b to be connected in parallel with each other. Then, the voltage resulting from the rectification of the low commercial AC voltage is smoothed by the capacitors 8a and 8b connected in parallel, and the smoothed voltages are applied to inverters 14a and 14b connected in parallel with the capacitors 8a and 8b, respectively, where they are converted into high-frequency voltages. The high-frequency voltages from the inverters 14a and 14b are transformed by of voltage transformers 18a and 18b, respectively, and the transformed voltages are rectified by output-side rectifiers 20a and 20b and smoothed by smoothing reactors 26a and 26b. The rectified and smoothed voltage appearing between output terminals 28P and 28N is applied to a load (not shown).
When one of the voltages in the higher commercial AC voltage group, other than the highest voltage of 575 V, is applied to the power supply input terminals 1a-1c, it is rectified in the input-side rectifier 3. The switch control unit 30 makes a judgment that the high commercial AC voltage other than 575 V is applied, which causes the thyristor 10 to be turned on. This causes the normally-closed switch 12a to be closed and causes the normally-open switches 12b and 12b to be opened. This, in turn, causes the capacitors 8a and 8b to be connected in series with each other. The high voltage resulting from rectifying the high commercial AC voltage is applied across the series combination of the capacitors 8a and 8b. In the same manner as described above with respect to the low commercial AC voltage applied to the power supply input terminals 1a-1c, a corresponding DC voltage is developed between the output terminals 28P and 28N for application to a load.
When the commercial AC power supply providing a voltage of 575 V, which is the highest one of the higher AC voltage group in the example being discussed, is applied to the power supply input terminals 1a-1c, it is rectified in the input-side rectifier 3. The switch control unit 30 detects the 575 V commercial AC power supply being used, and the thyristor 10 is turned off. The normally-closed switch 12a is closed, and the normally-opened switches 12b and 12c are opened, which results in connecting the capacitors 8a and 8b in series with each other. An IGBT 5 of a voltage-lowering converter 4, which is formed of, in addition to the IGBT 5, a flywheel diode 6 and a smoothing reactor 7, is so controlled by the voltage-lowering converter control unit 9 as to couple a lowered, rectified voltage across the series combination of the capacitors 8a and 8b. The magnitude of the rectified voltage across the capacitor series combination is the same as the one applied when the second highest one of the higher AC voltage group, i.e. 460 V in the example being discussed, is applied to the power supply input terminals 1a-1c. In the same manner as described above with respect to a lower voltage applied to the power supply input terminals 1a-1c, a DC voltage is developed between the output terminals 28P and 28N for application to the load.
When one of the voltages in the lower voltage group, namely, 200 V, 208 V, 230 V or 240 V, is applied to the power supply input terminals 1a-1c, the magnitude of the voltage applied across the parallel combination of the capacitors 8a and 8b is equal to the input AC power supply voltage multiplied by {square root over (2)}. For example, the voltage applied across the parallel combination of the smoothing capacitors 8a and 8b is about 280 V when the commercial AC power supply providing a voltage of 200 V is connected to the input terminals 1a-1c. When the input commercial AC power supply voltage is 240 V, the magnitude of the voltage applied across the capacitor parallel combination is about 340 V.
When one of the voltages in the higher voltage group except for the voltage of 575 V, namely, 380 V, 400 V, 410 V or 460 V, is applied to the power supply input terminals 1a-1c, the magnitude of the voltage applied across each of the serially connected capacitors 8a and 8b is equal to the input AC power supply voltage multiplied by {square root over (2)}/2. For example, the voltage applied across each of the smoothing capacitors 8a and 8b connected in series is about 270 V when the commercial AC power supply providing a voltage of 380 V is connected to the input terminals 1a-1c. When the input commercial AC power supply voltage is 460 V, the magnitude of the voltage applied across each capacitor is about 325 V.
The voltage-lowering converter 4 is so arranged as to develop an output voltage of 460 V multiplied by {square root over (2)}, which is about 650 V, when the commercial AC voltage of 575 V is applied to the power supply input terminals 1a-1c. Therefore, a voltage of about 325 V is applied across each of the capacitors 8a and 8b connected in series with each other.
With the described arrangement, readily available general-purpose semiconductor devices which can deal with a maximum voltage of 340 V can be used as the semiconductor switching devices of the inverters 14a and 14b, for dealing with lower and higher voltages of various magnitudes.
In some countries or areas, such as U.S.A. and Japan, lower commercial AC voltages of 100 V and 115 V are adopted. When a DC power supply apparatus of the above-described type is used in such countries or areas, the smoothing capacitors 8a and 8b are connected in parallel with each other, and, therefore, the voltage across each of the smoothing capacitors 8a and 8b is 100 V or 115 V multiplied by {square root over (2)}, i.e. about 140 V or about 160 V. Accordingly, a voltage of the magnitude required by a load cannot be developed between the output terminals 28P and 28N.
In other words, the DC power supply apparatus described thus far cannot deal with all of the lower commercial AC voltages on the order of 100 V, the lower commercial AC voltages on the order of 200 V, the higher commercial AC voltages of about two times the 200 V order voltages and higher.
Therefore, an object of the present invention is to provides a DC power supply apparatus for arc-utilizing apparatuses which can be used with various commercial AC power supplies supplying commercial AC voltages including the lower voltages on the order of 100 V.
A DC power supply apparatus for arc-utilizing apparatuses according to the present invention has power supply input terminals adapted to receive one of a first AC voltage, a second AC voltage having a magnitude about two times the first AC voltage, and a third AC voltage having a magnitude two or more times as large as the second AC voltage. The first AC voltage may be one of a plurality of commercial AC voltages provided by a first group of commercial AC power supplies. The second AC voltage may be one of a plurality of commercial AC voltages provided by a second group of commercial AC power supplies, and the third AC voltage may be one of a plurality of commercial AC voltages provided by a third group of commercial AC power supplies.
Two inputs of a rectifying unit are connected to the power supply input terminals for receiving and full-wave rectifying the AC voltage applied to the power supply input terminals. The resultant output voltage of the rectifying unit is applied to a voltage-lowering converter, which develops a predetermined lowered voltage between output terminals thereof. A bypass switch provides a bypass between the input and output of the voltage-lowering converter.
First and second capacitors are connected in series between the output terminals of the voltage-lowering converter. A switch circuit is connected between the junction of the first and second capacitors and one of the input terminals of the rectifying unit. A DC-to-high-voltage converter converts a DC voltage across the series combination of the first and second capacitors into a high-frequency voltage, which, in turn, is voltage-transformed by a transformer. A high-frequency-to-DC converter converts the high-frequency voltage from the transformer into a DC voltage.
When the first AC voltage is applied to the power supply input terminals, a controller operates to turn on or close the bypass switch, to turn off the voltage-lowering converter, and to turn on the switch circuit. Then, part of diodes of the rectifying unit, the switch circuit and the first and second capacitors form a full-wave type, voltage doubler rectifier circuit.
If the voltage applied to the power supply input terminal is the second AC voltage, the controller operates to turn on the bypass switch, to turn off the voltage-lowering converter, and to turn off the switch circuit. When the third AC voltage is applied to the power supply input terminals, the controller turns off the bypass switch, turns on the voltage-lowering converter and turns off the switch circuit.
When the first AC voltage is applied to the power supply input terminals of the DC power supply apparatus of the present invention, the switch circuit and the bypass switch are turned on, and, therefore, the rectifying unit operates as a full-wave voltage-doubler rectifier circuit. Accordingly, a voltage equal to the first AC voltage multiplied by 2xc3x97{square root over (2)} is applied across the series combination of the first and second capacitors.
When the second AC voltage is applied, the switch circuit is turned off and the bypass switch is turned on. Therefore the rectifying unit full-wave rectifies the second AC voltage, and a voltage equal to the second AC voltage multiplied by {square root over (2)} is applied across the series combination of the first and second capacitors. Since the magnitude of the second AC voltage is about two times that of the first AC voltage, the respective voltages applied across the series combination of the first and second capacitors when the first AC voltage and the second AC voltage are applied to the power supply input terminals differ little.
With the third AC voltage applied to the power supply input terminals, both the bypass switch and the switch circuit are turned off, and the voltage-lowering converter is turned on. Therefore, a voltage resulting from full-wave rectifying the third AC voltage is applied to the voltage-lowering converter, which, then, develops a voltage lower than the voltage applied to the power supply input terminals. The lower voltage is applied across the series combination of the first and second capacitors.
As described, the DC voltage applied to the DC-to-high-frequency converter is approximately the same, and, therefore, the DC voltage the load requires can be supplied to the load whichever one of the first, second and third AC voltages is applied to the power supply input terminals.
The controller may include a voltage detector. The voltage detector detects the first, second or third AC voltages applied to the power supply input terminals and develops a voltage representative signal, namely, a first AC-voltage representative signal, a second AC-voltage representative signal or a third AC-voltage representative signal. In this case, a selection signal generator and a coincidence judgement device are also used. The selection signal generator has a selector or operating device with which a user can select a selection signal corresponding to one of the first through third AC voltages. The selection signal is applied to the coincidence judgement device, to which the voltage representative signal is coupled, too. The coincidence judgement device causes the bypass switch and the voltage-lowering converter to be turned off when the voltage representative signal and the selection signal are not coincident.
With the above-described arrangement, the DC power supply apparatus does not operate when the intended voltage is different from the voltage actually coupled to the power supply input terminals.
The controller may be so arranged as to cause the coincident judgement device to turn off the bypass switch and the voltage-lowering converter when the voltage representative signal does not coincide with the selection signal, and also to cause the bypass switch and the switch circuit to be turned on and the voltage-lowering converter to be turned off when both of the voltage representative signal from the voltage detector and the selection signal from the selection signal generator are representative of the first AC voltage.
With this arrangement, the DC power supply apparatus does not operate if the AC voltage coupled to the power supply input terminals of the apparatus is not the voltage from which the user intends to operate the apparatus. Thus, an erroneous operation can be avoided. Also, if the user intends to operate the power supply apparatus from the first AC voltage, and the AC voltage coupled to the input terminals is actually the first AC voltage, the apparatus can operate normally.
The controller may be so arranged that it causes the coincidence judgement device to turn off the bypass switch and the voltage-lowering converter when the AC voltage represented by the voltage representative signal from the voltage detector is not coincident with the AC voltage represented by the selection signal from the selection signal generator, and causes the coincidence judgement device to turn on the bypass switch and turn off the switch circuit and the voltage-lowering converter when the voltage representative signal corresponds to the selection signal.
With this arrangement, when the user intends to operate the DC power supply apparatus from one of the first through third AC voltages and if the voltage which actually is coupled to the input terminals is different voltage, the DC power supply apparatus is prevented from operating. If the voltage intended to operate the apparatus from is the second AC voltage when the second AC voltage is coupled to the power supply input terminals, the DC power supply apparatus can operate normally.
The controller may be so arranged that it causes the coincidence judgement device to turn off the bypass switch and the voltage-lowering converter when the voltage represented by the voltage representative signal from the voltage detector and the selection signal from the selection signal generator are different, and causes the coincidence judgement device to turn off the bypass switch and the switch circuit and turn on the voltage-lowering converter when both the voltage representative signal and the selection signal correspond to the third AC voltage.
Thus, if the voltage actually applied to the power supply input terminals of the DC power supply apparatus is not the voltage the user intends to operate the DC power supply apparatus from, the apparatus is prevented from operating, and if the third AC voltage is being applied to the power supply input terminals when the user intends to operate the power supply apparatus from the third AC power supply voltage, the DC power supply apparatus can operate normally.
The controller may include a coincidence judgement device as well as the above-described voltage detector and the selection signal generator. The coincidence judgement device receives the voltage representative signal from the voltage detector and the selection signal from the selection signal generator. The coincidence judgement device causes the bypass switch and the switch circuit to be turned on and cause the voltage-lowering converter to be turned off when both of the voltage representative signal and the section signal correspond to the first AC voltage. The coincidence judgement device causes the bypass switch to be turned on and causes the switch circuit and the voltage-lowering converter to be turned off when the voltages represented by the voltage representative signal and the selection signal are the second AC voltage. If both of the voltage representative signal from the voltage detector and the selection signal from the selection signal generator represent the third AC voltage, the coincidence judgement device causes the bypass switch and the switch circuit to be turned off, and causes the voltage-lowering converter to be turned on. If the voltage represented by the voltage representative signal is different from the voltage represented by the selection signal, the coincidence judgement device controls the selection signal generator to make the selection signal correspond to the voltage representative signal from the voltage detector.
With this arrangement, if the voltage intended to be used differs from the voltage being applied to the power supply input terminals, the selection signal is changed to correspond to the voltage at the power supply input terminals so that the DC power supply apparatus can operate normally. Accordingly, even when the user cannot identify the voltage actually coupled to the power supply input terminals of the apparatus, the DC power supply apparatus can operate normally.